In optical fiber communication systems, in order to increase the volume of information transmittable through one optical fiber, it is known that using a multicore optical fiber including a plurality of cores and a cladding surrounding the outer circumferential surfaces of the plurality of cores, a plurality of signals is transmitted by light beams propagating through the cores.
However, in the multicore optical fiber, it is known that a group differential delay occurs between cores, i.e. skew occurs. Patent Literature 1 below describes a multicore optical fiber that reduces such skew. In this multicore optical fiber, cores adjacent to each other have the different propagation constants, and the skew between signal light beams propagating through a plurality of cores is 1 ps/m or less.
[Patent Literature 1] JP-A-2013-228548